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A greenhouse (or glasshouse) is a building where plants are cultivated. A greenhouse is built of glass or plastic; it heats up because the sun's incoming electromagnetic radiation (particularly infrared light) warms plants, soil, and other things inside the building. Air warmed by the heat from hot interior surfaces is retained in the building by the roof and wall.
The glass used for a greenhouse works as a selective transmission medium for different spectral frequencies, and its effect is to trap energy within the greenhouse, which heats both the plants and the ground inside it. This warms the air near the ground, and this air is prevented from rising and flowing away. This can be demonstrated by opening a small window near the roof of a greenhouse: the temperature drops considerably. Greenhouses thus work by trapping electromagnetic radiation and preventing convection.
Greenhouses are often used for growing flowers, vegetables, fruits, and tobacco plants. Bumblebees are the pollinators of choice for most greenhouse pollination, although other types of bees have been used, as well as artificial pollination.
Mowing young tobacco in greenhouse of half million plants ( Hemingway, South Carolina)
Besides tobacco, many vegetables and flowers are grown in greenhouses in late winter and early spring, then transplanted outside as the weather warms. Started plants are usually available for gardeners in farmers markets at transplanting time.
Greenhouses are increasingly important in the food supply of high latitude countries. The largest greenhouse complex in the world is at Leamington, Ontario (close to Canada's most southern spot) where about 200 acres (0.8 kmē) of tomatoThe tomato is a plant in the Solanaceae or nightshade family. The taxonomic name is either Solanum lycopersicum or Lycopersicon esculentum depending on the reference. Originating in South and Central America, the tomato is now grown world-wide for its bries are entirely grown under glass.
Greenhouses protect crops from too much heat or cold outside, shields plants from dust storms and blizzards, and helps to keep out pests. Light and temperature control allows greenhouses to turn unarable land into arable land. Greenhouses can feed starving nations where crops can't survive in the harsh deserts and arctic wastes. Hydroponics can be used in greenhouses as well to make the most use of the interior space.
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